1. Most printers will have a heated bed, I don't think you'll see much to differentiate there. Print speed is definitely a consideration as well as print bed size. Print temperature is a consideration if you're doing ABS or the higher temp filaments. This is where you need to ask yourself what will you be printing? Most desk toys don't care what filament you're printing with, tool box organizers won't care, parts you can print for a quarter probably won't care...
A lot of the 3D - 2A crowd are printing glock receivers in PLA+.
2. Most of my prints are PLA, I have done some PETG and TPU but they are rare. Heat resistance is a consideration, I haven't put any prints out in my car on a hot day, the dog leash holder I printed for the back porch has been there over a year in the weather and is just PLA and has held up fine, when it finally breaks I'll reprint it for $0.25 and move on. I did print a part for my dishwasher and it survived for over a year before it broke printed in PLA.
3. If you're printing higher temp filaments then yes to enclosed bed. I messed with ABS at one point and the bed temp really had to be up there, I made an enclosure to help hold heat but the material was such a pain I didn't do much with it.
My preferences for material PLA+ > TPU > PETG, I haven't messed with ASA from what I've read it's similar to ABS for printing. I don't have any outdoor/high temp print requirements that would justify it yet. When I printed with PETG and ABS the bed temp is way more critical than with PLA, material liked to curl if bed temp wasn't high enough with PETG, I think I was also printing slower with PETG.
Just some printing temps to throw out there these are in Celcius
PLA - about 200 degrees
ASA/ABS - about 250 degrees
PETG - 220 to 260